The Gela Basin Pockmark Field in the Strait of Sicily
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EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Biogeosciences, 10, 4653–4671, 2013 Open Access www.biogeosciences.net/10/4653/2013/ Biogeosciences doi:10.5194/bg-10-4653-2013 Biogeosciences Discussions © Author(s) 2013. CC Attribution 3.0 License. Open Access Open Access Climate Climate of the Past of the Past Discussions The Gela Basin pockmark field in the strait of Sicily (Mediterranean Open Access Open Access Sea): chemosymbiotic faunal and carbonate signaturesEarth System of postglacial Earth System Dynamics Dynamics to modern cold seepage Discussions M. Taviani1,2, L. Angeletti1, A. Ceregato1, F. Foglini1, C. Froglia3, and F. Trincardi1 Open Access 1ISMAR-CNR Istituto di Scienze Marine, Via Gobetti 101, 40129, Bologna, Italy Geoscientific Geoscientific Open Access 2Woods Hole Oceanographic Institution, 266 Woods Hole Rd, Woods Hole, Ma. 02543, USAInstrumentation Instrumentation 3 ISMAR-CNR Istituto di Scienze Marine, Largo Fiera della Pesca 2, 60125, Ancona, Italy Methods and Methods and Correspondence to: M. Taviani ([email protected]) Data Systems Data Systems Discussions Open Access Received: 10 December 2012 – Published in Biogeosciences Discuss.: 22 January 2013 Open Access Revised: 24 April 2013 – Accepted: 23 May 2013 – Published: 12 July 2013 Geoscientific Geoscientific Model Development Model Development Abstract. The geo-biological exploration of a pockmark brachia sp.), and 9609.5 ± 153.5 yr cal BP (L. kazani). One Discussions field located at ca. 800 m below sea level in the Gela basin shell of M. amorpha in core MEDCOR81 (pockmark#6, ◦ 0 00 ◦ 0 00 Open Access (Strait of Sicily, Central Mediterranean) provided a relatively Lat 36 45 38.89 N, Long 14 00 07.58 E, 822Open Access m below sea diverse chemosymbiotic community and methane-imprinted level) provided a sub-modernHydrology age of and 484 ± 54 yr cal BP. Hydrology and carbonates. To date, this is the first occurrence of such a type These ages document thatEarth fluid seepageSystem at this pockmark Earth System of specialised deep-water cold-seep communities recorded site has been episodically sustaining thiotrophic macroben- from this key region, before documented in the Mediter- thic communities since the end ofSciences the Younger Dryas stadial Sciences ranean as rather disjunct findings in its eastern and west- up to sub-recent times. Discussions Open Access ernmost basins. The thiotrophic chemosymbiotic organisms Open Access recovered from this area include empty tubes of the vesti- Ocean Science mentiferan Lamellibrachia sp., loose and articulated shells of Ocean Science lucinids (Lucinoma kazani, Myrtea amorpha), vesicomyids 1 Introduction Discussions (Isorropodon perplexum), and gastropods (Taranis moer- chii). A callianassid decapod (Calliax sp.) was consistently Pockmarks are circular to sub-elliptical crater-like depres- Open Access found alive in large numbers in the pockmark mud. Their sions of variable size (few to many hundredsOpen Access of metres in post-mortem calcified parts mixed with molluscs and subor- diameter) and depth (up to few tens m) typically due to de- Solid Earth dinately miliolid foraminifers form a distinct type of skele- gassing of fluids through fine-grainedSolid Earth unconsolidated marine Discussions tal assemblage. Carbonate concretions display δ13C values sediment under a variety of geologic scenarios (King and as low as −40 ‰ PDB suggesting the occurrence of light McLean, 1970; Hovland, 1989, 1992; Scanlon and Knebel, hydrocarbons in the seeping fluids. Since none of the truly 1989; Kelley et al., 1994; Gay et al., 2003; Trincardi et Open Access Open Access chemosymbiotic organisms was found alive, although their al., 2004; Paull et al., 2007). Pockmarks often occur in skeletal parts appear at times very fresh, some specimens clusters and cover wide areas, representing a common and The Cryosphere 14 widespread feature onThe the Cryosphere continental margins worldwide have been AMS- C dated to shed light on the historical evo- Discussions lution of this site. Lamellibrachia and Lucinoma are two of (Hovland and Judd, 1988). They receive much attention the most significant chemosymbiotic taxa reported from var- especially because escaping fluids are often hydrocarbon- ious Mediterranean cold seep sites (Alboran Sea and Eastern enriched venues in the form of slow seepage, vigorous vent- basin). Specimens from station MEDCOR78 (pockmark#1, ing or even eruptions, at times representing a distinct geo- Lat. 36◦46010.1800 N, Long. 14◦01031.5900 E, 815 m below hazard for offshore constructions and navigation (Newton et sea level) provided ages of 11736 ± 636 yr cal BP (Lamelli- al., 1980; Hovland, 1987; Curzi et al., 1988; Curzi, 2012). Such fluid releases are also considered as a potential co-actor Published by Copernicus Publications on behalf of the European Geosciences Union. 4654 M. Taviani et al.: The Gela Basin pockmark field in the strait of Sicily Fig. 1. Map showing the shaded relief Digital Terrain Model (DTM of 20 m resolution with 10× vertical exaggeration) of the Gela Basin in the Strait of Sicily. The figure illustrates the location of the pockmarks field discussed in this article (red spots represents major pockmarks); inset, the Mediterranean basin with rectangle showing the same area magnified in the figure. in triggering mass-sediment failure along continental mar- formation about resident chemosymbiotic communities, bio- gins, in conjunction with sea level changes or earthquakes sedimentological processes, authigenic carbonates and seep- (Minisini and Trincardi, 2009). Pockmarks are known to host age temporal variability in this sector of the Mediterranean at times peculiar biota in response to nature of escaping flu- Sea connecting its western and eastern basins. ids, rate of emissions, seepage resilience and water depth (Hovland and Thomsen, 1989; Hovland and Judd, 1988; Taviani, 2011, 2013). Gas charged sediments may in fact 2 Material and methods sustain microbiological communities operating on common The study area was surveyed during cruises HERMES05 compounds in fluids, i.e. hydrogen sulphide and hydrocar- (July 2005), MEDCOR and DECORS December 2009 and bons like methane (Cavanaugh et al., 2006; Dando, 2001; August 2011, respectively, of R/V Urania. Swath bathymetry Duperron, 2010). In turn, such communities could be ex- data were acquired using a Kongsberg Simrad EM710 ploited by specialized metazoans through complex symbiotic multibeam echosounder with a nominal sonar frequency of relationships (see MacDonald et al., 1990; Olu-Le Roy et 70–100 kHz an angular coverage sector of 140◦, a beam al., 2007; Taviani, 2001; Duperron, 2010, with references). width of 1◦ × 1◦ and 800 soundings per ping in dual mode. Pockmarks are also sites were methane-related authigenic Chirp-sonar profiles were obtained using a hull-mounted carbonates could be generated (Hovland et al., 1987; Hov- sixteen-transducer source with a sweep modulated 2–7 kHz land and Judd, 1988; Gontharet et al., 2007). outgoing signal equivalent to a 3.5 kHz profile. In the frame of the EU Hermes and Hermione projects, Bottom samplings were performed using a 1.2 ton gravity the Strait of Sicily in the central Mediterranean was targeted corer, large volume grab and epibenthic hauls (Table 1). as a key area to study sediment instability processes that af- Water-column attributes were measured with a Conductiv- fect continental margins. During such exploration a field of ity/Temperature/Depth profiler (CTD) using a Seabird SBE pockmarks was charted and sampled in detail off the south- 11 PLUS employing the SEASAVE V5.33 software. ern margin of Sicily (Fig. 1). Here we present first data on deep sea pockmarks in the Gela basin resulting in novel in- Biogeosciences, 10, 4653–4671, 2013 www.biogeosciences.net/10/4653/2013/ M. Taviani et al.: The Gela Basin pockmark field in the strait of Sicily 4655 Table 1. Sampling station list of Cruises MEDCOR and DECORS in the Gela Basin. Station Date Start Lat. Start Long. End Lat. End Long. Start End Gear GGMMSS.XX GGMMSS.XX depth depth MEDCOR-68 19 Dec 2009 36◦45038.2400 14◦00009.0200 820.0 CTD MEDCOR-69 19 Dec 2009 36◦45037.8300 14◦00008.2000 824.0 Grab MEDCOR-70 19 Dec 2009 36◦45016.4200 14◦01001.0700 840.8 Gravity Core MEDCOR-71 19 Dec 2009 36◦45016.0700 14◦00058.7900 36◦45035.0000 14◦00010.8200 840.0 820.0 Epibenthic modified haul MEDCOR-72 19 Dec 2009 36◦45015.1100 14◦01001.1800 36◦45015.6900 14◦01000.6100 842.0 840.6 CTD (POM) MEDCOR-74 19 Dec 2009 36◦45038.8200 14◦00010.3500 36◦44030.700 13◦58048.0600 824.0 850.0 Epibenthic modified haul MEDCOR-75 21 Dec 2009 36◦45048.4100 14◦01015.2900 833.0 Grab MEDCOR-76 21 Dec 2009 36◦45034.5600 14◦00024.8500 820.2 Grab MEDCOR-77 21 Dec 2009 36◦45044.5700 13◦58052.7900 831.7 Grab MEDCOR-78 21 Dec 2009 36◦45040.1300 14◦00008.9000 36◦46010.1800 14◦01031.5900 815.0 811.0 Epibenthic modified haul MEDCOR-80 19 Dec 2009 36◦45031.1800 13◦59054.5700 36◦45040.1000 13◦590.49.7900 820.0 815.0 Epibenthic modified haul MEDCOR-81 19 Dec 2009 36◦45037.8400 14◦00008.2100 832.0 Gravity Core MEDCOR-82 19 Dec 2009 36◦45016.2800 14◦01001.0800 840.9 Grab DECORS-48 8 Aug 2011 36◦46016.8600 14◦00006.8000 816.0 CTD DECORS-49 8 Aug 2011 36◦45039.2400 14◦00006.6400 818.0 Grab DECORS-50 9 Aug 2011 36◦46016.8600 13◦55028.4200 827.0 Grab Stable isotope analyses were performed at the Mass port complex in the area, has affected the northern mar- Spectrometry Laboratory of the CNR-IGG (Institute for gin of the basin mobilising a volume of sediment in the Geosciences and Earth Resources) Pisa, using a Finnigan- order of 1000 km3 in mid-Pleistocene times (Trincardi and MAT252 mass-spectrometer.